The invention relates to the field of the injection molding of items with plastic material.
In the state of the art, devices are known which are intended to be provided on presses to perform the molding of items through the injection of pressurised liquid plastic material. Such devices generally include mold elements which are movable with respect to each other and jointly cooperating by delimiting therebetween on the one hand joint planes and on the other hand a cavity intended to be filled with a liquid plastic material through injection channels with a view to form said item after ejection from the mold. When the production concerns items including, on at least one face, a protruding peripheral part such as a bossing or a lip provided with an edge for the connection with another adjacent face, the joint plane is tangent to such other face. In this case, it is necessary to carry out a subsequent machining of the item at said edge with a view to eliminating the flash produced at the joint plane and to obtaining the dimensions imposed by the specifications, for example by making a chamfer. Now this operation is difficult since it is carried out manually and requires specific tools on a work station which must be secured.
Conventional molding devices are thus often the origin of numerous problems relating to the quality and reliability upon the utilization of the item, more particularly when it is a technical part such as a sealing gasket. As a matter of fact, machining then concerns a functional area of the part which may have serious effects if it is not carefully inspected.
The present invention aims at solving the technical problems met by the prior art in a simple and efficient way. This goal is reached, according to the invention, using a device for the injection molding characterized in that it includes a mold element to form the protruding part of the item, whose plane of connection with the immediately adjacent front mold element is angularly oriented from said edge and on at least a portion of the length thereof according to the direction of ejection. Thanks to the invention, the joint plane is shifted out of the protruding functional part which has no more flash when the item is ejected from the mold. The subsequent machining of this part is no longer necessary then.
According to an advantageous characteristic, said joint plane is oriented along an angle between 10° and 80° with respect to the axis of symmetry of the cavity. According to another advantageous characteristic, said mold element of the protruding part has a draft intended for the molding of the protrusion connected to the joint plane frontwards through a chamfer extending up to said edge. Preferably, said front mold element has a plane face perpendicular to the axis of symmetry of the cavity. According to a specific alternative solution, said mold elements and said cavity have rotation symmetry about the axis of said cavity. According to another alternative solution, said mold element of the protruding part has a globally tapered shape.
In a particular embodiment of the invention proper to the production of items having two protruding parts each having an edge, the device then includes a central mold element providing the molding of the second protruding part and having a joint plane with said front mold element angularly oriented from said second edge and at least on a portion of the length thereof, according to the direction of ejection. In this case, said mold element of the first protruding part is a side element whose plane of connection with said central mold element is inclined rearwards and towards the axis of symmetry of said cavity. According to still another advantageous characteristic, said injection channels are arranged through the front mold element. Another object of the invention is a method for the production of an item of the type including at least one protruding peripheral part provided with an edge for the connection with the front face thereof, using the molding device according to the invention. Still another object of the invention is the utilization of the device of the invention to produce an item such as a simple or double lip annular sealing gasket made of elastomer.
The device and the method according to the invention make it possible to simplify the operations of the molding production of an item having at least one protruding functional part. In addition, the invention makes it possible to improve productivity and cost efficiency of industrial facilities since the output of the press supplying the power no longer depends on the frequency and duration of the subsequent machining operations which have become useless. The deviations in dimensions which existed, on the one hand, between the batches of produced items and, on the other hand, on the same item between the various protruding parts because of the additional operations of deflashing and finishing are no longer necessary, since such operations are eliminated and the items already have correct dimensions when leaving the mold. The risks of deterioration in the quality of the items and more particularly the edge area which resulted from the wear of machining tools and more particularly cutting tools are significantly reduced. Eventually, the invention makes it possible to avoid chips resulting from the deflashing operations which were the sources of pollution on the industrial site and to save energy by eliminating the need for machining stations.
For clarity, identical or similar elements are referred to using identical reference numbers on all the figures.